1. Field of the Invention
This invention relates to a mask defect measurement method and mask quality determination method for measuring a phase defect of a semiconductor exposure mask or the like used for exposure by the use of EUV in a blank mask state. In addition, the present invention relates to a manufacturing method of the semiconductor device that uses the above-mentioned method.
2. Description of the Related Art
A semiconductor exposure mask used for exposure by the use of EUV is a reflecting mask. The mask has a structure in which two types of layers having different reflectances called a multilayered film are alternately laminated on a glass substrate, a film called an absorber is formed on the multilayered film and then a circuit pattern is formed by processing the absorber. If particles are present on the glass substrate when the multilayered film is formed, the multilayered film formed thereon is locally upheaved or subsided. Since an area (phase defect) in which the phase of the reflected light is disturbed occurs, there occurs a problem that the area will be transferred onto a wafer at the exposure time. Therefore, it is necessary to check whether a phase defect is present or not in a state called a blank mask state set before the absorber is formed.
As the technique for checking the presence of a phase defect of the blank mask, a method for specifying the position of the defect by irradiating the blank mask with EUV and detecting scattered light produced when a defect is present on the blank mask is proposed (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2003-114200). However, since the size of a phase defect is generally considerably smaller than that of a CCD pixel, it is difficult to specify the shape of the phase defect based on a detected signal. If the CCD pixel is formed sufficiently small, the minimum size of a defect whose shape can be specified becomes smaller. However, since the time required for checking phase defects on the entire surface of the mask is inversely proportional to the size of the CCD pixel, the checking cost will increase. Further, even if the CCD pixel is made small, it is difficult to obtain information associated with the height of the phase defect.
Further, a method for focusing reflected light of light incident on the blank mask onto a detecting portion, blocking a portion of the reflected light by means of a shielding plate disposed in an intermediate portion of the optical path and detecting irregularity of the blank mask based on the intensity of the reflected light obtained by the detecting portion is proposed (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2003-4654). With this technique, the defect detecting operation and the shape specifying operation can be performed by means of the same device. However, only whether the defect is concave or convex can be determined and a problem that the shape measurement cannot be sufficiently made occurs.
Further, a defect checking method of EUV mask blanks by using a Schwarzschild optics is proposed (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2007-171640). However, this technique is to output the importance of a defect (the level of a risk of transfer) based on the angular distribution of the intensity of scattered light and is not a method for specifying the shape of a defect. That is, the technique is to output a proportion of the shapes of defects to be transferred among the shapes of defects estimated based on the angular distribution. For example, if half of the estimated shapes of defects are transferred, the transfer risk is set to 50% and if none of the estimated shapes of defects is transferred, the transfer risk is set to 0%. Therefore, in a case other than the risk of 0 or 100%, it becomes impossible to correctly determine whether the defect will be transferred or not.